This disclosure relates to a treated fabric that is comprised of splittable conjugate fibers and to a process for modifying such a fabric to enhance its dyed appearance. More specifically, the present invention relates to a consolidated nonwoven fabric containing continuous filaments comprised of polyester and polyamide components, in which at least portions of the polyamide component have been removed. The process used to remove portions of the polyamide component involves treating the fabric with acid. The result is a dyed fabric that has a deeper depth of shade and that has a brighter hue, as compared to the untreated fabric. Contemplated end uses of such a dyed fabric are also provided.
Microdenier fabrics are traditionally created by mechanically or chemically splitting a conjugate fibers into its elementary filaments. Microdenier fabrics, particularly those having polyamide and polyester components, are traditionally difficult to dye, often resulting in a fabric with a xe2x80x9cfrostyxe2x80x9d appearance. This appearance is due to the inability to effectively dye the polyamide component.
As will be discussed herein, the present process is applicable to any conjugate fibers that includes a polyamide as one of its components. The present process improves the dyed appearance of fabrics of any construction (woven, knit, or nonwoven) that are comprised of microdenier yarns that result from splitting conjugate multi-component yarns. Although the benefits of this process are readily apparent on a specific nonwoven fabric that will be discussed in detail herein, it should be understood that it is equally applicable to woven or knitted microdenier fabrics created from splittable yarns.
Nonwovens are known in the industry as an alternative to traditional woven or knit fabrics. To create a nonwoven fabric, a filament web must be created and then consolidated. Staple fibers are formed into a web through the carding process, which can occur in either wet or dry conditions. Alternatively, continuous filaments, which are formed by extrusion, may be used in the formation of web. The web is then consolidated, and/or bonded, by means of needle-punching, thermal bonding, chemical bonding, or hydroentangling. A second consolidation treatment may also be employed.
A preferred substrate for the present disclosure is a nonwoven formed of continuous splittable filaments that are extruded as a web and then consolidated. The continuous conjugate filaments are obtained by means of a controlled spinning process. The continuous filaments have the following characteristics: (1) the continuous filaments are comprised of at least two elementary filaments and at least two different fiber types; (2) the continuous filaments are splittable along at least a plane of separation between elementary filaments of different fiber types; (3) the continuous filaments have a filament number (that is, titer or yarn count) of between 0.3 dTex and 10 dTex; and (4) the elementary filaments of the continuous filament have a filament number between 0.005 dTex and 2 dTex. Simply put, the nonwoven fabric can be described as a nonwoven fabric of continuous microfilaments. Such a fabric is described in U.S. Pat. Nos. 5,899,785 and 5,970,583, both to Groten et al., each of which is incorporated herein by reference.
A wide range of synthetic materials may be utilized to create the elementary filaments of the continuous conjugate filaments. However, the present invention is intended to improve the characteristics of fabrics that contain elementary filaments of different fiber types (e.g., polyesters and polyamides). As such, the group of polymer materials forming the elementary filaments may be selected from among the following groups: polyester and polyamide; polyolefin and polyamide; polyurethane and polyamide; polyester, polyolefin, and polyamide; aliphatic polyester and aromatic polyester; and acrylic polymers and polyamides.
However, the fabric described in the above-referenced patents is not readily dyeable to dark shades. Although it is known in the art to selectively dye components of conjugate filaments, the ease with which such dyeing may be accomplished and the depth of shade which may be achieved have not been heretofore adequately addressed. The treated nonwoven of the present disclosure addresses these issues.
In a preferred embodiment, the present process involves subjecting the microdenier fabric to a degrading treatment, which degrades a portion of one component of the conjugate yarns, and then to dyeing. The degrading treatment, given certain reaction kinetics, removes at least a portion of one component of the conjugate filament. For a polyester/polyamide conjugate, an acid treatment is used to remove at least a portion of the polyamide component. The at least partial removal of the polyamide component, especially on the surface of the fabric, results in a fabric having enhanced dyed appearance. In an alternate embodiment, treatment with a basic solution after the acid treatment may be employed to enhance the hydrophilic nature of the fabric for purposes of enhancing moisture transport.